A face mill is previously known by U.S. Pat. No. 4,743,144. However, in this face mill, the cutting edges and the chip surfaces connecting to the same are archedly curved or circular. This means that the active cutting edge—depending on the rise of the curvature or arc line—will cut more or less deeply into the surface being machined, and thereby give rise to marked, concave chutes in the completed surface (see FIG. 11 of U.S. Pat. No. 4,743,144). In other words, the surface finish becomes far from optimum, in particular when the milling inserts are circular and the arc line of the individual cutting edge has a great rise. Another disadvantage of the known face mill is that the milling inserts thereof have a negative cutting geometry, i.e., the front and back sides have identical shape and size, whereby any given generatrix along the arched chip surface extends perpendicular to the front side as well as to the back side. This means that the material to be released will be pushed (rotationally) in front of the chip surface and rather be pressed into the surface of the workpiece than being cut away or stripped from the same. Another disadvantage of the face mill disclosed in U.S. Pat. No. 4,743,144—which is shown equipped with a plurality of milling inserts—is that the individual milling insert is detachably mounted in a seat in a cassette, which in turn is semi-permanently fixed in a peripheral pocket in the basic body, more precisely by a screw joint. In contrast to such mills in which the seats of the milling inserts are recessed directly in the proper basic body, cassettes of that kind give rise to a plurality of problems, among other things a complicated and expensive manufacture of the face mill in its entirety as well as an awkward adjustment of the milling inserts with the purpose of locating all active cutting edges in exactly one and the same plane. In this connection, the mere existence of a plurality of cassettes, which cannot for sure be mounted completely immovable in the basic body, constitutes risky sources of error.
A face mill having principally the same design as the face mill according to U.S. Pat. No. 4,743,144 is furthermore known by JP 52-35160. In this case, the active cutting edges of the milling inserts are per se straight and situated in a common plane. Serious disadvantages of this face mill are, however, on one hand, that the negative radial angle of the cutting edges is very limited (smaller than 45°), and on the other hand that the effective rake angle of the milling inserts, i.e., the angle between the chip surface of the individual milling insert and the plane surface to be generated is negative, i.e., smaller than 90°. The limited negative radial angle means that the milling insert will be subjected to very great stresses, not only when the same enters the workpiece but also after that. This in combination with the negative rake angle makes the milling insert blunt-cutting, the sheared off metal material tending to be pressed inward/downward against the unmachined surface rather than to be brought in the direction away from the same. In addition, the force required for the feed of the mill becomes comparatively great.
The present invention aims at obviating the above-mentioned disadvantages of the face mill previously known. An object of the invention to provide a face mill that has the capacity of removing a thin surface shell from workpieces having slightly or moderately uneven surfaces while producing a finish-machined surface having an extraordinary high surface finish. In the applications intended for the face mill, the cutting depth is incidental and may in practice be maximized to approx. 0.5 mm, wherein a surface finish of down to 1 μm should be attainable.
Another object of the invention is to provide a face mill that can operate with short machining operations per machined surface unit; all with the ultimate purpose of reducing the cost of the machining operation in question to a minimum. Furthermore, the replaceable milling inserts of the tool should not only be easy-cutting with the purpose of allowing fast cutting processes, but also strong to ensure an optimum service life and good machining economics.
Yet another object of the invention is to provide a face mill that can be equipped with a large number of milling inserts without imminent risk of the same being erroneously mounted in relation to the plane or the line along which the even surface is to be generated. Also the manufacture of the face mill as well as the handling of the same should be effectable in an efficient and economic way.